1. Field of the Invention
The present invention relates to a method and an apparatus for detecting obstructions to a motor-powered window movement. More particularly, the invention relates to a method and an apparatus for detecting sensitively, accurately and at high speed obstructions that may occur to a power window device during its movement without increasing a memory capacity needed for the function.
2. Description of the Related Art
Various systems have been proposed to detect obstructions that may occur to a power window device during its operation on board the vehicle. One such system is disclosed in conjunction with a power window device in Japanese Published Unexamined Patent Application No. Sho 61-60981.
The disclosed power window device utilizes a motor load current value as the parameter by which to detect obstructions to a motor-powered window movement. The entire movable range of the window is divided into a plurality of portions. Each divided moving area is set beforehand with a reference current value indicating whether or not an obstruction to the window movement has occurred. In operation, a detected motor load current value is compared with the reference current value. If the detected motor load current exceeds the reference current significantly, an obstruction to the powered window movement is judged to have occurred.
In the above power window device, the reference current value for each divided moving area is established on the basis of a peak motor load current in effect when no obstruction takes place during the window movement (opening/closing) throughout the area in question.
Other power window devices are known to adopt a motor torque value as the parameter by which to detect obstructions to the motor-powered window movement.
Unlike the power window device of Japanese Published Unexamined Patent Application No. Sho 61-60981, power window devices utilizing the motor load torque for reference do not divide the entire movable range of the window into multiple portions to establish a reference value for each divided moving area. As such, these power window devices have difficulty in accurately detecting obstructions to the powered window movement.
The power window device disclosed in Japanese Published Unexamined Patent Application No. Sho 61-60981 detects obstructions to the motor-powered window movement using the peak motor load current as the parameter for the detection. What takes place upon detection is as follows: when the motor driving voltage, i.e., the output voltage of the battery on board the vehicle, deviates from a rated output voltage, the motor load current fluctuates in its peak. If noise is overlaid for some reason on the detected motor load current at its peak, the peak motor load current fluctuates likewise.
In such cases, a reference value for each divided moving area of the window is set on the basis of the peak motor load current in effect when no obstruction occurs to the window movement throughout the area in question. It follows that the reference value necessarily contains some error. When the potentially erroneous reference value is used as the basis for detecting obstructions to the powered window movement, faulty judgments tend to occur: an obstruction can be detected where there is none, or a snagged window movement may not be detected where the window is actually jammed.
The cited power window device of Japanese Published Unexamined Patent Application No. Sho 61-60981 apparently meets the demand for enhanced levels of the detection of obstructions to the window movement by dividing the entire movable range of the window into a larger number of portions. However, the increased number of divided moving areas entails a growing number of data items to be addressed and stored: more reference medians to be set for the divided areas, more motor load current values to be detected for each divided area, etc. The data need to be stored by resorting to an increased memory capacity. This translates not only into a power window device of an enlarged scale but also into higher production costs.